Among display panels, such as liquid crystal display panels, reflection of external light at the surface is unfavorable. If the reflectance of external light at the surface is large, images of a viewer himself, objects that are placed around the panel, lighting devices, etc., are reflected in the panel surface, deteriorating the visibility of display. Particularly in a bright environment, excessive reflection of external images occurs. One of the existing solutions to this problem is to provide a low reflection structure at the surface of the display panel such that the reflection of external light is reduced.
As a low reflection structure which reduces the reflection at the surface of the display panel, an antireflection technique which utilizes a so-called “moth-eye” structure has been disclosed (see Patent Documents 1 and 2). By providing an antireflection film which has a moth-eye structure at the surface of the display panel, the reflectance of external light at the surface of the display panel is decreased to about 1% or lower.
However, even if the reflection at the surface of the display panel is reduced, reflection may occur, or the contrast ratio of display may decrease, due to light reflected inside the display panel. Therefore, it is desired to decrease the reflectance inside the display panel independently of reduction in reflectance at the surface of the display panel, preferably together with reduction in reflectance at the surface of the display panel.
The internal reflection of the display panel is now described with an example of a liquid crystal display panel. The liquid crystal display panel includes a pair of substrates and a liquid crystal layer interposed between the substrates. One of the pair of substrates includes pixel electrodes and TFTs that are in a matrix arrangement, and bus lines, for example. This substrate is hereinafter referred to as “TFT substrate”. The other substrate includes a counter electrode, a color filter, and a light blocking layer (black matrix). This substrate is hereinafter referred to as “counter substrate”. Typically, the counter substrate is placed at the viewer side of the liquid crystal layer. In the example liquid crystal display panel described hereinbelow, the counter substrate is placed at the viewer side of the liquid crystal layer.
External light impinging on the liquid crystal display panel is partially reflected by a surface of the liquid crystal display panel which is in contact with the air (outermost surface). In other words, external light impinging on the liquid crystal display panel is reflected at the interface between the counter substrate and the air. Usually, the counter substrate has a polarizer at the viewer side, and therefore, the reflection occurs at the interface between the surface of the polarizer and the air. In this specification, reflection by the surface of the liquid crystal display panel which is in contact with the air (hereinafter, simply referred to as “the surface of the liquid crystal display panel”) is referred to as “surface reflection”. Light transmitted through the surface of the liquid crystal display panel is partially reflected by the counter substrate and the TFT substrate. In this specification, reflection other than the surface reflection is referred to as “internal reflection”.
The applicant of the present application discloses, in Patent Document 3, a substrate which includes a light blocking layer that has a low reflectance and which is suitably used as a color filter substrate of a liquid crystal display panel. This substrate includes a light blocking layer which includes a high optical density layer and a low optical density layer. The optical densities and refractive indices of the respective layers are adjusted such that reflection which is attributed to a conventional light blocking layer (also known as “black matrix”) is reduced.